In an ink jet printer, ink is supplied to a printer head which has a plurality of nozzles for ejecting droplets of ink onto a sheet of paper or the like to print words, pictures, etc. The characteristics of the ink droplets, such as the size, shape, velocity and frequency and stability of the droplet formation effect the characteristics of the lines, etc. which are printed. Therefore it would be desirable to be able to measure the various characteristics of ink droplets as ejected from a printer head to be able to determine how to control the printer head to achieve a print of desired characteristics.